Year of Award

2024

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Ecology and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Thomas E. Martin

Commitee Members

Zachary A. Cheviron, Angela D. Luis, John L. Maron, Bret W. Tobalske

Publisher

University of Montana

Abstract

Examining why species vary in behavior and life history strategies is a fundamental part of ecology and evolution. Yet, due to the difficulties of quantifying behavior in the field, we know surprisingly little about how species spend their time and energy daily, why interspecific differences occur, and what are the physiological and demographic consequences of these differences. In this dissertation, I use songbirds to examine the influence of ultimate selection pressures (e.g., mortality risk) and proximate ecological conditions (e.g., temperature) on foraging and reproductive behavior. I also examine the influence of reproductive behaviors on fitness correlates (e.g., body mass, reproductive productivity, survival).

In my first chapter, I examined why species vary in how active and conspicuous they behave while foraging. My results show that shorter-lived species have faster and conspicuous movement lifestyles which maximize food acquisition to fuel their fast and risky life histories. Conversely, long-lived species have slow and inconspicuous lifestyles which fit with the reduced food needs of risk-averse and slower life history strategies.

In my second chapter, I examined influences on the timing and frequency of parents provisioning their offspring. I found that high provisioning rates which decrease over the day was a common strategy for species with low adult survival and low nest predation, which can maximize reproductive success by provisioning offspring most when they are hungriest. Consistently low provisioning rates over the day was a common strategy for species with high nest predation and/or high adult survival, a strategy which can reduce predation risk and energetic costs to parents.

In my third chapter, I tested hypotheses to explain why birds often rapidly lose mass during reproduction. Path analysis and a nest heating experiment provided evidence that mass loss was not related to reproductive effort. My results thus support mass loss being an adaptive strategy to increase foraging and flight efficiency with no apparent fitness costs.

Collectively, this dissertation describes bird behavior in often unprecedented detail, helps to understand the causes of differences in foraging and parental care strategies between species and individuals, and interprets the significance of these differences within a conceptual life history framework.

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© Copyright 2024 Timothy Robert Forrester